Control system for reversible hydraulic motors



Jan. 6, 1953 F. B. LEVETUS CONTROL SYSTEM FOR REVERSIBLE HYDRAULICMOTORS 2 SHEETSSHEET 1 Filed June 28, 1951 Inventor FRMvc, S s W 5Attorney 5 Jan. 6, 1953 F. B. LEVETUS 2,624,321

CONTROL SYSTEM FOR REVERSIBLE HYDRAULIC MOTORS Filed June 28, 1951 2SHEETSSHEET 2' a; s 5 L F/GSM a 5 1. L3

r J HQ 4 4/? 3 N N302: F

' N2 /v N.

Inventor FRg/ic'ys a. LEVPYvS x E I, u

Attorney 5 Patented Jan. 6, 1953 CONTROL SYSTEM FOR REVERSIBLE HYDRAULICMOTORS Francis Benjamin Levetus, Allesley, Coventry, England, assignorto The Keelavite Company Limited, Allesley, Coventry, England, a companyof Great Britain Application June28, 1951, Serial No. 234,067 In GreatBritain April 24, 1950 7: Claims. 1.

This invention. relates to control systems for reversible hydraulicmotors of the kind having inlet-and outletports the functions of whichare interchangeable by a reversing valve apparatus to reverse the motor,the reversing valve apparatus being so constructed anda-rranged that itcanat will be caused to connect either of the twome'tor p'ortsto' asource of hydraulic pressure andthe other toarelief passage or reservoirso as to cause the motor to be driven in one direction or the other, andin which the pressure supply'passage by which the hydraulic fluid isdelivered to the reversing" valve-has an automatic pressure-operatedreliefvalve therein which is maintained openautomatically when the fulldeli-veryefthe-s'ource of hydraulicfluid under'pre'ssure is notbeingutilized by' the motor so as to pass theexcessive hydraulic fluidthrough a relief passage back to the hydraulic receiver and yet maintainthe required pressure'in the hydraulic supply passageat all times.

The object of the present invention is to provide an improvedcontrolsystem of the above general kind which will be simple in construction;will require a minimum number of separate valves ofsimple form and'willyet'meet allpraotical requirements including" that of ensuring as far aspossiblethat for any given setting of a control valve the speed of themotor will remain substantially constant irrespective of the load.

A control system for a reversible hydraulic motor having inlet andoutlet ports the functions of which are reversecl'to reverse the motoraccording to the present" invention comprises. a pressure supplypassagearranged" to be connected to a source of hydraulic pressure, a reversingvalve controlling the flow of hydraulic fluid to the motor from thepressure supply passage and from the motor to. a. relief passage orreservoir and arranged so that in a neutral positionit connects each ofthe portsof the motor to a relief passage while when moved from suchneutral positionin one direction or the other it progressivelydisconnectsone or other of the ports of the motor from its reliefpassage and connects that port to the pressure supply passage, and apressure responsiverelief: valve in thepressure supply pas? sage thevpressure responsive member of which is arranged. to respond to thepressure diiferencein matically' to whichever of these two ports is atthe moment at the higher pressure,

Conveniently the pressure responsive relief valve comprises a pressureresponsive piston member one face of which is subject to pressurederived from the pressure supply passage while the other face is subjectto the pressure in a chamber which is connected to the cha-nge -overvalve and through it to the motor port at the moment at higher pressure,the chamber which derives pressure from the pressure sup-ply pas:- sagehaving. also aport therein coaxial with the piston and leading to arelief passage, this, port being controlled by a part formed integral"with or connected to the piston and. acting as the relief valve member.Preferably the relief valve is of the kind. forming, the subject ofUnited States patent application Serial No; 190g4l'20, now abandoned, sothat the pressure difference on its pressure responsive member or:piston necessary to maintain it open. under any conditions issubstantially the same as: that required to cause it to open fromitsclose'd position, that is to say the opening of the: valve does notb'ring into effect any additional areas on which act unbalanced Ipressures tending to: open or close the valve;

The form of the reversingvalve apparatus may vary but conveniently thevalve is of the known type comprising a valve cylinder with anintermediate point-in the length of which thepressure supply passagecommunicates continuously through a pressure-supply port whilerelief-ports communicate continuouslywith the oppositeends of thecylinder and inlet and outlet port'slead to themotor inlet and outletports respectivelyfrom points in the cylinder situated intransverseplanes on opposite sides of the pressure supply port, and a valve memberof the piston type comprising a central portion of reduced cross-sectionforming" with the surroundinggpart of the cylinder a pressure chamberinto which the pressure supply port opens continuously and end ortionswhich fit the cylinder and control the inlet andoutlet port's'so as toenable either'on'e'of the two ports to be brought into communicationwiththe pressure chamber'while the other is" in communication throughthe-adjacent end of the cylinder with its associated relief port. Whensuch a valve is used with the present invention the disposition'anddimensions of theports and'of the end portions of the valve member aresuch that when the valve member occupies a neutral position itsend-portions serve respectivelyto-cutoff the inlet and outlet parts fromthe pressure chamber and maintain themvin communication respectivelywith the relief ports at the ends of the cylinder, whereas movement ofthe valve member from this neutral position in one direction or theother causes one or other of the end portions thereof progressively tocut off the port controlled by it from its associated relief port and tobring it progressively into communication with the pressure chamber.Moreover the formation of the ends of the valve member and/or of theinlet and outlet ports controlled thereby is preferably such that therate of progressive opening and closing of the inlet and outlet portswith movement of the valve member is such as to provide sensitivecontrol of the operation of the motor and preferably such that the rateof movement of the valve throughout its movement is approximatelyproportional to the rateof opening and closing of the ports.

The invention may be carried into practice in various ways but one formof control system according to the invention is illustrated by way ofexample in the accompanying drawings in which,

Figure 1 is a diagram showing diagrammatically the apparatusconstituting the complete control system with the hydraulic pump andmotor with which it is associated,

Figure 2 is a side elevation partly in section of the valve assemblyincorporated in the system,

Figure 3 is a plan view of the valve assembly shown in Figure 2, partlyin section on the line 3--3 of Figure 2,

Figure 4 is an end elevation of the valve assembly shown in Figures 2and 3, and

Figure 5 is a sectional view of the valve assembly shown in Figures 2, 3and 4 taken on the broken line 5-5 of Figure 4.

The apparatus constituting the control system shown in Figure 1comprises a pressure supply passage A to which hydraulic fluid isdelivered under pressure continuously by a constant delivery pumpindicated at A In permanent communication with the pressure supplypassage A is a pressure-operated relief valve B including a valve part Bcontrolling a relief port B and a piston part B operating within acylinder C with its upper face subject to the pressure in the passage Awhile its lower face is subject to the pressure in a passage D and tothe force of a spring C so that the valve B will open whenever apredetermined difference occurs between the pressures respectively inthe passages A and D.

. While the valve B is shown diagrammatically for simplicity ofillustration in Figure 1 in a form in which the piston surface subjectto the pressure in the passage A is smaller than that subject to thepressure in the passage D, the valve would in fact be constructed, forexample, in the manner described hereinafter with reference to Figures 2to 5 so that the effective piston area on which the pressure in thepassage A acts is substantially equal to the effective piston area onwhich the pressure in the passage D acts, so that the Valve will openautomatically whenever the pressure in the passage A exceeds that in thepassage D by a predetermined amount sufficient to cause the valvemembers B, B and B to move downward against the action of the spring CThe valve B thus acts to maintain a pressure in the passage Arepresenting a predetermined difference between the pressuresrespectively in the passages A and D.

The pressure supply passage A leads to a pressure supply port E enteringthe cylinder E of a control valve at approximately the centre of itslength while the ends of the control valve cylinder are provided withrelief ports E E communicating with a relief passage F which leads,preferably through a reservoir F to the inlet side of the pump A Thevalve cylinder E is also provided with inlet and outlet ports E*, Ecommunicating respectively through passages G, G with the inlet andoutlet ports G G of a reversible hydraulic motor G The control valvecylinder E contains a piston type control valve member 0 hereinaftermore fully described which in its central or neutral position maintainsthe ports E and E in continuous communication respectively with theports E and E whereas movement of the valve member in one direction orthe other from this neutral position progressively shuts 01fcommunication between one of the ports E and E and its associated port Eor E and brings it into communication with the pressure supply port E.

Extending between the passages G and G is a passage H in which isarranged an automatic change over valve in the form of a ball H arrangedin a valve chamber H having seatings H H as its ends by way of which thechamber communicates respectively with the passages G and G andintermediate port H leading to a passage J which communicates by way ofa small leak orifice indicated at K and a passage K with the lower endof the cylinder 0 and also with a spring pressed ball valve Lcontrolling a port leading to the relief passage F. Thus, the ball valveH will be forced into engagement with one or Other of the two seatings HH according to which of the two passages G and G happens at the momentto be at higher pressure so as to connect the high pressure one or thesetwo passages always automatically to the passage J. The flow throughthis passage J will be small by reason of the small metering orifice Kbut sufiicient, whenever working pressure exists in one or other of thepassages G, G to cause the valve L to be lifted, thus maintaining apredetermined pressure in the passage D and hence in the deliverypassage K and in the lower end of the cylinder C whenever workingpressure exists in one or other of the passages G, G While alsopermitting the relief valve B to open at a considerably lower pressureand thus largely relieve the pressure in the passage A when bothpassages G and G are connected to their respective relief ports E and. E

In the practical construction of valve assembly shown in Figures 2 to 5the various valves are all arranged within a single structure and forconvenience the parts of this practical structure corresponding to thevarious parts indicated diagrammatically in Figure 1 are identified bythe same reference letters as in that Figure 1.

Thus the complete valve assembly comprises a main casing M ofapproximately rectangular form with a subsidiary casing M formed ormounted thereon so as in effect to form part thereof.

Leading from the main casing M, as shown, are the passages G, G thepassage F and the passage A, and formed within the casing are the twocylinders E and C and a chamber containing the ball valve L, whileformed in the subsidiary casing M is the chamber H of the change-overvalve.

The cylinder E is formed as shown with five annular recesses N, N N Nand N communicating with the ports E E, E, E and E respectively, asillustrated in Figure 1, of which N and N communicate with the passage-F(N directly and N through a passage in the casing M (not shown)). Therecesses N and N communicate by passages H, H respectively with ports MM respectively at opposite ends of the chamber H whilev the recess Ncommunicateswith the passage A.

Mounted to slide in the cylinder E is a piston type, control valvemember having three waisted or reduced portions 0 O 0 which, when thevalve member is in its neutral position, as shown, lie respectively inthe recesses N, N and N*,, as shown in Figure 5. Each of the reducedportions. 0 and O has, in addition, leading from it towards the reducedportion 0 a channel O and these channels. 0 when the valve member isinits neutral position, maintain communication respectively between the.recesses N and-;N and between the recesses N and N The reduced portion,0 is, on the contrary, prqvided with frusto conical extensions 0 which,when the valve member is in its neutral position, terminatejustshort of,the adjacent ends of the recesses N and N One; end of the valve member 0is connected through a link P to a control P by which it can thus bemoved longitudinally, while its other end extends into a cylindricalchamber P and carries a piston-like member P having a conical recess inits circumferenceinto which isadapted to beforced a, spring pressed ballP when the valve member occupies its neutral position so as not only tohold it inthat position against unintentional displacement but toindicate to an operator by feel when it occupies that position.

The cylinder C contains the relief valve 13, comprising thepiston part13 and a valve part, B whichco-operates with a seating in the adjacentendof a tubular insert Q around a portlB therein leading to a reliefchamber Q between the outer wall of, said insert and cylinder C, whichrelief chamber in turn communicates with the recess N and hence at alltimes with, the passage F. The tubular insert Q also, serves as a guidefor a/rodlike extension B on the valve part 13 The valve member B ishollow, the, end of the bore of the extension B being open whilethe'opposite end of the bore is closedby a valve Q normally maintainedupon, its seat by a spring C which thus alsoacts-on the valve member band tends always to maintain the valve partB upon, its seating. Th borealso opens by way of lateral passages into the chamber Q within thecylinder, C on the side-of thepiston B remote from the spring C whichchamber is in open communication at all times with the recess N? andthereby with the pressure supply A.

The chamber Q in which the spring C lies communicates by way of apassage R with a chamber R which is closed at one end and communicatesat its other end through the spring pressed valve L with a chamber L inopen communication through the relief chamberv Q with the recess N' andpassag F. The. spring L acting on the valve L is adjustable by means ofan adjustable abutment L of known general type.

The chambers R and Q are in continuous.

communication through the passage K a small meteringOrificeKandthe'passageJ with an intermediate point in the length of thechamber H in which the change-over valve H liesbetween the two seatingsH and H by way of which seatings the chamber communicates respectivelywith passages H, H leading respectively to the recesses N N Thus thevalve H is moved into engagement with one or the other of the seatings1-1 or H according to whether one or the other of the recesses N or N isat the higher pressure at J and K are thus also connected to the reliefassage Fand there is therefore no appreciable fluid" pressure in thechamber Q The relief valve 3, B will thus maintain in the recess N andpassage A a pressure only suiiicient to over-come the force of thespring C When the control valv member 0 is moved to the left in Figure 5from its neutral position it will be seen that it first closescommunication between the recess N and the recess N through the adjacentgroove 0 and then progressivelyopens communication between the recess Nand the recess N as the adjacent frusto-conical part 0 moves into therecess N The recess N -and hence the passage G is thus progressivelyconnected to the pressure supply passage A so that pressure fluid issupplied to the port G of the motor G At the same time the passage M ispressurised'so that th change-over valve H is moved into engagement withthe seating H and pressure fluid is thus delivered through the meteringorifice K and passage K to the chamber Q The relief valve L is so setthat it opens if this pressure exceeds a predetermined value such thatwith-the pressure in the chamber Q at that predetermined value, thevalve B will open at the maximum permissible working pressure in thparts of the system which during operation are subiect to the workingpressure.

Thus the motor G is brought into operation in one direction and suchoperation is under sensitive control by means of the lever P If it isdesired to caus the meter (E to operatein the opposite direction, thecontrol valve member O is moved to the right in Figure 5 from itsneutral position so that the recess N is cut off from the recess N andthen progressively brought into communication with the recess N The portG of the motor G is thus supplied with pressure fluid under'the controlof the valve 0, the changeover valve H being caused to engage theseating H so that the chamber Q is brought into communication with therecess N by way of the'passage M the chamber H the passage J, themetering orifice K and the passage K and the pressure conditions in theapparatus are thus the same as when the valve 0 is moved to the leftfrom its neutral position.

The valve Q acts as a safety valve to permit escape of fluid from thechamber Q into the chamber Q 'and thence through th valve L in the eventof very sudden rises in pressure.

What I claim as my invention and desire to secure icy-Letters Patent is:

l. A control system for a reversible-hydraulic motor having inlet andoutlet ports the functions of which are reversed to reverse the motor,comprising a pressure supply passage arranged to be connected to asource of hydraulic pressure, a reversing valve controlling the flow ofliquid to the motor from the pressure supply passage and from the motorto a relief passage or reservoir and arranged so that in a neutralposition it connects each of the ports of the motor to a relief passagewhile when moved from such neutral position in one direction or theother, it progressively disconnects one or other of the ports of themotor from its relief passage and connects that port to the pressuresupply passage, a pressure-responsive relief valve in the pressuresupply passage having a pressure-responsive member which responds to thepressure difference in two chambers, one of said chambers being subjectto pressure derived from the hydraulic pressure supply passage, andautomatic change-over valve means by which the other of said chambers isconnected to whichever of the two ports of the motor is at the moment atthe higher pressure, said change-over valve means including a pressureresponsive valve member subject to pressure derived respectively fromsaid two motor ports and automatically movable -by the pressuredifference acting thereon to cause said means to function.

2. A control system for a reversible hydraulic motor as claimed in claim1, in which the pressure-responsive relief valve is in the form of apiston one face of which is subject to the pressure in the pressuresupply passage while its other face is subject to the pressure in thechamber which is connected to the change-over valve means and through itto the motor port at the moment at higher pressure, the chamber whichderives pressure from the pressure supply passage having also a porttherein coaxial with the piston and leading to a relief passage, thisport being controlled by a part formed integral with or connected to thepiston and acting as the relief valve member.

3. A control system for a reversible hydraulic motor as claimed in claim2, in which the pressure-responsive relief valve includes pistonsurfaces of substantially equal area subject respectively to thepressures on the inlet and outlet sides of the valve and a springtending always to maintain the valve closed.

4. A control system for a reversible hydraulic motor as claimed in claim1, in which the reversing valve comprises a valve cylinder having a portat an intermediate point in its length communicating with the pressuresupply passage, relief ports at its opposite ends communicatingcontinuously with the relief passage and outlet ports situated in planesrespectively on opposite sides of the port communicating with thepressure supply passage and communicating respectively with the inletand outlet ports of the motor, and

said reversing valve also comprises a valve member of the piston typehaving a central portion of reduced cross-section forming with the valvecylinder a pressure chamber into which the pressure supply port openscontinually, and end portions which control the cylinder outlet portsand, when the valve member occupies a neutral position, serverespectively to cut off said cylinder outlet ports from the pressurechamber and maintain them in communication respectively with the reliefports at the ends of the cylinder, whereas movement of the valve memberfrom this neutral position in one direction or the other causes oneorother of the end portions thereof progressively to cut off the portcontrolled by it from its associated relief port and to bring itprogressively into communication with the pressure chamber.

5. A control system for a reversible hydraulic motor as claimed in claim4, in which the end portions of the valve member and the cylinder outletports are so formed that the rate of progressive opening and closing ofthe latter is substantially in proportion to the movement of the valvemember.

6. A control system for a reversible hydraulic motor as claimed in claim1 in which the pressure responsive relief valve comprises apressureresponsive piston member one face of which is subject to thepressure in the pressure supply passage while its other face is subjectto the pressure in a chamber which is connected to the change-over valveand through it to the motor port at the moment at higher pressure, thechamher which derives pressure from the pressure supply passage havingalso a port therein coaxial with the piston and leading to a reliefpassage, this port being controlled by a part formed integral with orconnected to the piston and acting as the relief valve member, and inwhich the reversing valve comprises a valve cylinder having a pressuresupply port at an intermediate point in its length with which thepressure supply passage communicates continuously, relief portscontinuously open at its opposite ends and outlet ports communicatingwith the inlet and outlet ports of the motor from points in the cylindersituated in planes respectively on opposite sides of the pressure supplyport, and said reversing valve also comprises a valve member of thepiston type having a central portion of reduced cross-section formingwith the valve cylinder a pressure chamber into which the pressuresupply port opens continually, and end portions which control the outletports and when the valve member occupies a neutral position, serverespectively to cut off the outlet ports from the pressure chamber andmaintain them in communication respectively with the relief ports at theends of the valve cylinder whereas movement of the valve member fromthis neutral position in one direction or the other causes one or otherof the end portions thereof progressively to cut off the port controlledby it from its associated relief port and to bring it progressively intocommuni REFERENCES CITED The following references are of record in thefile of this patent:

UNITED STATES PATENTS Number Name Date 2,057,088 De Millar Oct. 13, 19362,503,870 Harrington Apr. 11, 1950'

